JSV

We know when air is released it cools. If I have 10lbs of boost in the manifold does it cool when it is released in the cylinder.

tomcat

Good question. When air is compressed it heats up, when it expands it cools down. Two things complicate this matter when considering a supercharged engine.

First of all, since compressors aren't 100% efficient, they add more heat to the air than the heat of compression. This extra heat stays in the air even if it is allowed to expand. Second, the engine is a positive displacement device so the volume of the air is held constant, it doesn't get to expand. The cylinder is filled with air at 10 psi minus whatever pressure was lost overcoming the restriction of the port and valve.

JimV

Yabit when the piston is on it's way down that creates low pressure and we know high pressure moves towards low pressure if pressure was equal there would be no movement of air

tomcat

So the air does expand in the cylinder and there would have to be some amount of temperature reduction..I think. Is this amount of cooling significant compared to the cooling provided by evaporating fuel, I doubt it. And then the piston comes back up and squeezes everything up to 150 psi so temperature shoots up anyway. what are you thinking JSV?

JimV

What I am thinking is to try to enhance this in the port. I dont have any proof that it works. And if it does how effective. Sorry JSV is my home computer. When I was a kid my dad showed me what he called a vortex generator. The "in" side was compressed air that moved down a tube into a small chamber whear it split from both sides. At the two exits one side was so hot you couldn't touch it, the other side was so cold it frosted.

tomcat

I saw one of those in a textbook, I don't want to say how long ago. One application was to push cold air into a protective suit for hot work, like on a blast furnace. I forget how they work but the pressure differential was high, plant compressed air 60 -100 psi?

Now I have a question for you. I know "it depends" but what would you expect as a reasonable HP gain from porting for an engine that is already in the 600 HP range? I'm thinking 540 - 572 CID with good aluminum heads but unported. Is this a gain that can be realized without changing RPM (the camshaft) or do you always do both together? What would such an upgrade cost with the right components? Sorry, that's three questions.

JimV

Yes it kinda depends, the two examples I can give you would be KAAMA's 540s and a checkmate. We started out at 630hp @5500 with a mild chamber and bowl port. We upgraded the Dart 310cc heads to a full port and increased the compression to 10:1 from 9.2:1. We also changed the carb and camshaft. The motor made 699hp @5750

The second was a 540 that we went from the same bowl port to a full port, cut the heads to 10:1 and changed to the same cam as KAAMA's. He picked up 4mph or about 80 hp. If I had to guess I would say by porting stock heads you should see 40hp with no other changes.

I ported a ton of the stock 5.0 litre ford heads and it's about the same 40hp increase with some intake mods.

tomcat

That's a good answer. These examples suggest to me that an additional 10% is a reasonable expectation. I guess I'm thinking about the amount of money this would cost, and comparing it to the results and cost of my intercooler setup.